The disclosure of Japanese Patent Application No. 2002-136049 filed on May 10, 2002 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to a storage battery control apparatus and control method.
2. Description of the Related Art
A related-art storage battery control apparatus is described in Japanese Patent Application Laid-Open Publication No. 2000-23306. An electric power supply system for an electric vehicle, as a storage battery control apparatus described in this laid-open patent application, is designed for installation in an electric vehicle in which a vehicle-driving electric motor is driven by electric power from a main electricity storage or an engine generator. The main electricity storage is formed by a capacitor battery that has a plurality of series-connected electric double-layer capacitor cells. This system also has an auxiliary electricity storage for accessories.
If the voltage of any one of the capacitor cells reaches a set value, or if the charging operation time reaches a set value, or if the number of charge-discharge cycles reaches a set value, the power supply system charges the other capacitor cells using power from the auxiliary electricity storage, regenerative braking power, or power from the generator until the voltages of the other capacitor cells reach the set value. Thus, the system substantially equalizes voltages of all capacitor cells.
However, the related-art storage battery control apparatus releases stored charges if the voltage between the capacitor terminals reaches a set value. Therefore, if the capacitor internal resistance rises due to a temperature fall, the control apparatus performs discharge when some more charges can be stored into the capacitors. Such a discharge operation is not economical. In view of the above-described situations, it is an object of the invention to provide a storage battery control apparatus capable of increasing the amount of charges stored into a storage battery.
One aspect of the storage battery control apparatus of the invention is characterized by including: a first controller that releases charges stored in a capacitor that forms a storage battery if an inter-terminal voltage of the capacitor becomes equal to or higher than a predetermined threshold; a temperature detector that detects a temperature of the capacitor; and a second controller that changes the predetermined threshold in accordance with the temperature of the capacitor.
Therefore, if the inter-terminal voltage of the capacitor changes due to a change in temperature, unnecessary discharge is substantially avoided by changing the threshold. Hence, the amount of charges stored in the storage battery can be increased.
The second controller may increase the predetermined threshold as the temperature of the capacitor decreases. If the temperature of the capacitor becomes low, the capacitor internal resistance increases, and therefore, an increased amount of charges can be stored in the capacitor by raising the threshold.
The first controller may discharge the capacitor if the inter-terminal voltage of the capacitor reaches the predetermined threshold. Therefore, if the inter-terminal voltage of the capacitor reaches the predetermined threshold, the capacitor can be protected by discharging the capacitor.
Furthermore, it is also possible that the first controller does not discharge the capacitor until the inter-terminal voltage of the capacitor reaches the predetermined threshold. Therefore, a sufficient amount of charges can be stored in the capacitor by avoiding release of charges stored in the capacitor.
Still further, the storage battery may have a plurality of capacitors connected in series, and the first controller may perform discharge until amounts of charges stored in all the capacitors become substantially equal. Greater amounts of charges can be stored if the differences among the amounts of charges stored in the capacitors are less or nil. Therefore, if a plurality of capacitors are connected in series, the above-described construction allows storage of a greater amount of charges.
Still further, if the inter-terminal voltage of any one of the capacitors reaches the predetermined threshold, the first controller may release charges stored in the capacitor whose inter-terminal voltage has reached the predetermined threshold, on a basis of comparison with a value based on the amounts of charges stored in all the capacitors. Therefore, by performing discharge on the basis of comparison with a value based on the inter-terminal voltages of all the capacitors, the amounts of charges stored in the capacitors can be equalized. It is to be noted herein that the capacitor inter-terminal voltage is dependent on the amount of charges stored.
The storage battery control apparatus may further r include: a voltage detector that detects the inter-terminal voltage of the capacitor; a switch that allows a change of a state of connection between terminals of the capacitor; and a control circuit that is connected to the voltage detector, the temperature detector and the switch, and that turns the switch on and off so that discharge of the capacitor is controlled.
Therefore, the capacitor inter-terminal voltage can be detected by the voltage detector. Discharge can be performed by the control circuit turning on the switch on the basis of the measured value of the inter-terminal voltage and the temperature of the capacitor. Discharge can be prohibited by turning off the switch.
Another aspect of the storage battery control apparatus of the invention is characterized by including: a first controller that releases charges stored in a capacitor that forms a storage battery if an inter-terminal voltage of the capacitor becomes equal to or higher than a predetermined threshold; a temperature detector that detects a temperature of the capacitor; and a second controller that avoids setting the predetermined threshold if the temperature of the capacitor is lower than a predetermined temperature.
If the temperature becomes low, the capacitor internal resistance increases and therefore the allowable amount of charges stored decreases, so that the need for discharge reduces. Therefore, avoidance of the setting the threshold will considerably avoid unnecessary discharge, and will increase the allowable amount of charges stored, and will protect the capacitor, and will increase the total amount of charges stored.
An aspect of the control method of the storage battery control apparatus of the invention is characterized by including the steps of: releasing charges stored in a capacitor that forms a storage battery if an inter-terminal voltage of the capacitor becomes equal to or higher than a predetermined threshold; detecting a temperature of the capacitor; and changing the predetermined threshold in accordance with the temperature of the capacitor.
Another aspect of the control method of the storage battery control apparatus of the invention is characterized by including the steps of: releasing charges stored in a capacitor that forms a storage battery if an inter-terminal voltage of the capacitor becomes equal to or higher than a predetermined threshold; detecting a temperature of the capacitor; and avoiding setting the predetermined threshold if the temperature of the capacitor is low.